FIG. 1 is a schematic block diagram of a communication system comprising a host terminal 2 and an external wireless cellular modem 4, the modem 4 comprising an antenna 5. The host terminal 2 may be a user terminal, and may for example take the form of a desktop computer, laptop computer, tablet style computer, or mobile phone (which may be referred to as a “smart phone”). The modem 4 may for example take the form of a dongle for plugging into the host terminal 2. Alternatively the modem 4 may take the form of a mobile phone handset which, as well as being a conventional mobile telephone, can be connected to the host terminal 2 so as to act as an external cellular modem for the host terminal 2. The modem 4 is external to the host terminal 2 in that it is a separate unit housed in a separate casing, but which is connected or connectable to the host terminal 2 by means of a wired or wireless connection (as well as being removable or being able to be disconnected from the host terminal 2). In another alternative set up, the modem 4 could be internal to the terminal 4, e.g. taking the form of a wireless module in a desktop or laptop computer.
The system also comprises a mobile cellular network 6 such as a 3GPP network; and a further, packet-based network 8, such as a wide area internetwork such as the Internet. The mobile network 6 comprises a plurality of antennas 10, and a router 16 connecting between the mobile network 6 and the further, packet-based network 8 (a router connected in this manner may be called a gateway and could be considered a component of either or both the mobile network 6 and the further network 8, but for illustrative purposes is shown in the mobile network 6 in FIG. 1). The mobile network 6 further comprises a gateway support entity 7 operatively coupled to the antennas 10 and the router 16. For example the gateway support entity may be a GGSN (Gateway GPRS Support Node) in a 2G or 3G system, or an SAE (System Architecture Evolution) gateway in a LTE (Long Term Evolution) system. The GGSN 7 or other such node may comprise one or more access points, e.g. in the form of one or more instances of a suitable access point protocol such as one or more APNs (access point names).
For connecting to the 3GPP network 6 or other such cellular network, the modem 4 comprises first physical interface apparatus comprising a wireless transceiver, typically in the form of a radio frequency (RF) transceiver and an antenna 5. This interface apparatus of the modem 4 connects via an antenna 10 of the cellular network 6 to an access point of the gateway support entity, e.g. the GGSN 7. For example, if the mobile cellular network 6 is a 3GPP network, then the connection between the modem 4 and a 3GPP network may be called a PDP (Packet Data Protocol) context in 2G or 3G terminology, and an EPS (Evolved Packet System) bearer context in LTE terminology. The physical medium of the connection is typically a radio channel such as a 2G, 3G or LTE radio channel and the protocol that drives it may comprise a set of protocol layers as defined for example by 3GPP. Each of the one or more access points of the GGSN 7 then provides a connection onwards to the gateway router 16 and via that router to the Internet 8.
For connecting to the host terminal 2, the modem 4 comprises second physical interface apparatus. The second interface, between the host 2 and modem 4, could for example comprise a wired connector such as USB connector for plugging into the host terminal 2, or a short-range wireless transceiver such as an infrared connection or a radio frequency connection (e.g. Bluetooth) for connecting wirelessly to the host terminal 2 via a local wireless connection.
The host terminal 2 is installed with one or more applications 18 which when executed on the host terminal 2 send and/or receive communications over the Internet 8 via the first and second interface apparatuses, wireless cellular network 6 and the relevant gateway 16, via the established context, supported by the GGSN 7. The system allows the host terminal to access the Internet 8, e.g. using Internet Protocol version 6 (IPv6).
When a terminal accesses the Internet 8, e.g. to view a website or send an email, it uses a name-to-address resolution system such as a domain name system (DNS). A domain name is a human-recognizable name or label, typically a text string, which is meaningful to a user so as to identify an IP resource from the perspective of the user. For instance the resource could be a web site or an email destination, and the domain name could take the form “www.example.com” for a website or “example@example.com” for email. A domain name system is a naming system associating human-recognizable domain names with various information including a less user-friendly address or numerical identifier such as a numerical IP address. That is, the domain name system or other such name-to-address resolution system maps the human-recognizable name of an internet resource (that will be used by the user to identify the resource) to a computer-readable network address that identifies the location of the resource on the Internet or other such packet-based network (and that will be used by routers to identify the resource as a source and/or destination of a packet or message being sent to or from that resource).
In order to access a desired Internet resource, a user of the terminal inputs a domain name of the resource into an application running on that terminal such as a web browser or email client. The application or operating system then sends a name-to-address query in the form of a DNS query to a name-to-address resolution server in the form of a domain name server, e.g. a DNSv6 server in the case of IPv6. This kind of server is also sometimes just called a “name server”. A DNS server is a network entity responsible for resolving the translation of domain name into IP address, or recursively asking other name servers until full resolution is achieved. That is, when the DNS server receives a query from a terminal, it looks-up the queried domain name in its own records to determine whether it can resolve the query itself (either because it is the authoritative server for that domain name or because it has cached the result of a previous query). If so it returns a response comprising the corresponding IP address to the terminal that requested it. If the DNS server cannot resolve the request itself on the other hand, it may in turn contact one or more other DNS servers to query whether they can resolve the address. Once the required address is found, it is returned to the terminal. Some DNS servers 9 and 9′ are shown in FIG. 1, although it will be appreciated that many more would be present on the Internet 8 than are shown.
In order to make use of such a system, a terminal is typically configured with an address of at least one designated DNS server in which to send its DNS queries. In a 3GPP environment for example, the DNS server addresses are provided to the modem by the GGSN in Packet Configuration Option field of various messages such as Activate PDP Context Accept.